As new services such as video on demand, high-resolution television, and online games have been gradually proposed, the users' demand for bandwidth increases day by day. The development of fiber-to-the-home technology effectively ensures the bandwidth of “last mile” access network. A passive optical network (PON) technology is currently one of the most widely applied fiber-to-the-home technologies. Currently, the PON includes a broad PON (BPON), a Gigabit PON (GPON), and an Ethernet PON (EPON).
FIG. 1 is a schematic structural view of a PON network in the prior art. Various services of users are transmitted through access and transport networks in the PON, such that different telecommunication service nodes can be flexibly accessed for accepting services. As shown in FIG. 1, the PON includes optical line terminals (OLTs), optical network units (ONUs), and a passive optical splitter at a PON access layer and includes a transmission network and telecommunication service nodes at a metropolitan convergence layer. User equipment (UE) accesses the metropolitan convergence layer through the PON access layer. The OLTs and the passive optical splitter are connected through a trunk optical fiber. The passive optical splitter realizes point-to-multipoint optical power distribution and is connected to a plurality of ONUs through a plurality of branch optical fibers. The ONUs are connected to the UE. The trunk optical fiber, the passive optical splitter, and the branch optical fibers between the OLTs and the ONUs are generally referred to as passive optical distribution network (ODN). The transmission of data from the OLTs to the ONUs through the ODN is a downstream direction and the transmission of data from the ONUs to the OLTs through the ODN is an upstream direction.
In the PON, as the number of ONUs interconnected to the OLTs through the passive optical splitter is relatively small, a cover radius is not longer than 20 kilometers, such that the number of OLTs is relatively large to fulfill the demands of the UE in the PON architecture, the location areas thereof are also remote and dispersed, which is inconvenient for management and maintenance, and has a high cost in establishment and maintenance of the PON. With the emerging of a next generation optical access network, a technology of extending the PON from ONUs to 100-kilometer data transmission is proposed. The technology proposes the PON objectives of 10 Gbps symmetric rate data transmission, 100-kilometer transmission distance, and 1:512 split ratio. The utilized technology is mainly an optical power amplification and wavelength division technology. In the PON, the data transmission extension simplifies the levels of networks such as the PON access layers and metropolitan convergence layers, so as to decrease the number of the network nodes, increase the number of the UEs under the administration of a single OLT, allocate the cost to the greatest extent, thereby eventually reducing the equipment cost and saving the management and maintenance cost.
Currently, the data transmission extension in the PON may utilize regenerator extension solutions through an optical-electrical-optical (OEO) conversion manner. FIG. 2 is a schematic structural view of a data transmission extension network in a PON realized in an OEO manner in the prior art. An OEO extender box is set between the passive optical splitter and the OLTs. The OEO extender box is the OEO equipment. The OEO extender box divides conventional ODN into two ODNs, that is, an ODN 1 and an ODN 2. The OEO extender box is adapted to complete optical-electrical (O/E) conversion, burst reception, power amplification, and electrical-optical (E/O) conversion for the data of the OEO extender box and then send the processed data. Therefore, a power of the transmitted data does not gradually attenuate with the increasing of the transmission distance, such that the OLTs or ONUs receiving the data are unable to receive data.
As for the OEO extender box in FIG. 2, a specific setting location thereof is still in dispute. FIG. 3 is a schematic structural view of a specific configuration of an OEO extender box. That is, two OEO extender boxes are configured between the OLTs and the ONUs, in which one is located near the OLTs and the other is located near the passive optical splitter, that is, at the ONU side. However, the use of two OEO extender boxes is not economical. Another specific configuration of the OEO extender box is provided, that is, the OEO extender box is configured between the OLT and the ONUs, and the OEO extender box is configured near the OLT. However, this manner does not significantly improve the power budget.
FIG. 4 is a schematic view of a basic structure of an OEO extender box in the prior art. In an upstream direction, an O/E amplification shaping module, a burst-mode clock and data recovery (BCDR) module, and an E/O amplification module are included. In a downstream direction, an O/E amplification shaping module, a retiming module (including a CDR module), and an E/O module are included.
In the upstream direction, as the ONU usually uses a burst-mode optical component to send data, that is, to send burst data. In order to ensure the correct data receiving of the OEO extender box or the OLTs as a receiver, a preamble needs to be added in front of a frame head of each data frame of data. Therefore, in the upstream direction, after receiving a data frame, the O/E amplification shaping module in the upstream direction in the OEO extender box performs O/E conversion, amplification, shaping on the data frame, and sends the data frame to the BCDR module for performing the BCDR, and then the data frame is sent to the E/O amplification module for performing the E/O conversion amplification according to a recovered upstream clock and then the data frame is output. In the downstream direction, after receiving the data frame, the O/E amplification shaping module in the downstream direction in the OEO extender box performs O/E conversion, amplification, and shaping on the data frame, and the clock and data recovery is then performed on the data frame through retiming, and then the data frame is sent to the E/O module for E/O conversion through the recovered downstream clock and then the data frame is output.
In the implementation of the present invention, the inventors find that the prior art has the following problems. As the upstream direction involves receiving burst data, the O/E conversion, amplification, and shaping need to be performed, and the BCDR module is adapted to correctly identify, receive, and recover the clock data. However, during such processing, if it is ensured that each burst data frame after O/E conversion, amplification, and shaping is correctly received and the clock data can be recovered, a certain adjustment period is required, thereby resulting in preamble impairment of the data frame. If the data frame is sent after the BCDR module performs the BCDR on the data frame, a portion is missing from the preamble in the data frame. FIG. 5 shows a timing chart of burst reception and clock and data recovery performed on the data frame by the O/E amplification shaping module and the BCDR module. In an upper part of FIG. 5, the timing chart shows a data frame received by the OEO extender box, in which TDSR denotes a burst interval, Ton denotes invalid data sent in a starting process of a burst transmitter laser of the ONU within the time period, TLR denotes potential recovery time of the transimpedance amplifier and the limiting amplifier of the O/E amplification shaping module within the time period, and TCR denotes BCDR clock recovery time within the time period. The preamble of the data frame spans the TLR and the TCR, and a data part starting with a delimiter carried in the data frame is then followed. The subsequent part may also include residual parts of the preamble. In the lower part of FIG. 5, the timing chart of data frames after being processed by the O/E amplification shaping module and the BCDR module is shown, which includes an interval duration of bandwidth distribution, a preamble impairment duration, an unimpaired preamble duration, and a data part carried in the data frame. FIG. 5 shows a special situation in which all the preamble is consumed. Only the data parts carried in the data frame is left after the BCDR process performed by the BCDR module.
Therefore, the preamble impairment caused by O/E conversion, amplification, and shaping performed on the data frame by the O/E amplification shaping module and the BCDR performed on the data frame by the BCDR module may influence a subsequent receiver such as the OLTs or the subsequent OEO extender box in receiving the data frame correctly. For example, it is assumed that the preamble of the data frame has 44 bits. The O/E conversion, amplification, and shaping performed by the E/O amplification module and the BMCR process performed on the data frame by the BCDR module require 13 bits. In this case, the data frame only has a 31-bit preamble left. For subsequent OLTs that receive the data frame, the preamble of the data frame cannot satisfy the requirements on the byte number of the preamble specified in the protocol, such that the OLTs cannot correctly receive the data frame, and as a result, the OEO manner cannot actually realize data transmission extension.